1. Field of the Invention
This invention relates generally to linear measurement tools, and more particularly to a linear measurement system that is inexpensive and highly accurate.
2. Description of Related Art
The following art defines the present state of this field:
Huber et al., U.S. Pat. No. 5,131,017 describes an evaluation device with an absolute value counter providing an incremental position measuring system which determines absolute position even in case of loss of the main power supply. The evaluation device is operated by means of an emergency power supply operated by means of an emergency power supply while the main power supply is out. Following the restoration of the main power supply, counting pulses are supplied to a follow-up counter by a pulse emitter, until the follow-up counter has reached the counter reading of the absolute value counter. Two rectangular signals, which are phase-shifted by 90 degrees in relation to each other, are formed as a function of the counting signals, which are present at the evaluation device in the form of output signals.
Hiramoto, U.S. Pat. No. 4,698,828 describes a system for sensing the position of an object such as a rotating member. The system provides a plurality of photo-couplers coupled with the interposition of a rotary disc having slits and rotating with the object. The system further has a position signal generating circuit for receiving signals produced by the photo-couplers and producing a series of component position signals differing in phase successively by a predetermined phase difference, a counting circuit having an up/down count for determining the position of the object by counting occurrences of a predetermined change recurring periodically in the component position signals, and a direction determining circuit for producing an up/down counter. Each time the predetermined change occurs in any one of he component position signal, the direction determining circuit determines the order in which the change occurs in two successive component position signals.
Burkhardt, U.S. Pat. No. 4,229,647 describes an improved electronic counter for use with an incremental measuring device. The counter includes two or more individual counters, a display unit, and a switch for selectively connecting any one of the individual counters with the display unit. Each of the individual counters may be individually set to a separate zero point so that each counter may be used to store a position value in a separate frame of reference. The position value stored in any one of the individual counters may be switched to the display unit without disturbing the contents of the other individual counters. In the preferred embodiment, the counter includes a circuit for automatically resetting a first individual counter to zero whenever the measuring device senses a predetermined reference mark, thereby automatically maintaining a calibrated zero point in that counter. The preferred embodiment also included a power fail circuit which generates a warning signal when the measuring device is operated following an interruption in the line voltage used to power the device. This warning signal is maintained until the first individual counter is automatically reset, and the device is again calibrated for use.
Renner et al. U.S. Pat. No. 3,965,340 describes an apparatus relating to an optical counting apparatus, which is employed in combination with an electronic hand-held calculator. The structure of this invention greatly expands the use of the hand-held calculator by permitting such to be employed as a measuring device and a unit counter. An optical device is activated by the difference between transmission of light and darkness. This activation is used as a counting apparatus or a measurer of distances with the accumulated count or the distance measure to be read on the display unit of the calculator
Ohtsuka, U.S. Pat. No. 3,886,542 describes a member, on which are marked scales having respective different pitches between their graduations, and is movable past a graduation detecting position at which there are plural graduation detectors each operatively associated with a different respective scale. One scale has fine or "unit" graduations arranged successively in groups of ten, and another scale extending parallel to the first scale has coarse of "tens" graduations each corresponding to a respective group of fine graduations. Each tenth fine graduation is relatively elongated. The detectors cooperate, respectively, with the fine graduations, with the elongated fine graduations and the coarse graduations. A counter has plural digit positions, with one digit position being a "units" position and a next higher digit position being a "tens" digit position. An electronic switching circuit connects the detectors to the counter and is operable, responsive to movement of the scale bearing member past the detecting position at a relatively low speed, to supply, to the low digit position of the counter, input signals from the detector operatively associated with the scale having the fine graduations. The electronic switching circuit is operable, responsive to movement of the scale bearing member past the detecting position at a relatively higher speed, to supply, to the next higher digit position of the counter, input signals from the detector operatively associated with the coarse graduation scale. Switching between the two digit positions of the counter, responsive to a change in the speed of movement of the scale bearing member past the graduation detecting position, is effected only responsive to simultaneous detection of a relatively elongated fine graduation and the corresponding coarse graduation.
Nelle, U.S. Pat. No. 4,101,764 describes an incremental measuring instrument having a series of fixed reference marks along one edge of a grid scale in which a series of movable magnets are located along the opposite edge of the grid scale so that a magnet may be associated with each reference mark which is needed for control purposes in the particular application in which the system is being used. The magnets are movable mounted so that reference marks not needed for control purposes in any specific application do not have magnets associated with them. An electric switch, preferably a magnetically actuated Reed switch, is also provided in the system's sensor head. Electrical impulses generated by the magnets and the switch are transmitted to an electronic comparator along with electric impulses generated when the sensor head passes over the reference marks. This electronic comparator is connected to the system's electronic control counter when and impulse is simultaneously fed to the comparator by the switch associated with the magnets.
Blanchard, U.S. Pat. No. 4,215,337 describes a form of shaft-position encoder employing "fast" and "slow" rotary selectors coupled by gearing to each other and to a shaft whose position is to be encoded. The selectors cooperate selectively with elements in respective "fast" and the "slow" circular series of elements. Two counters register the number of pulses in a train varying in accordance with the number of elements in each of the "fast" and the "slow" series between one end of the series and an element in cooperation with a related selector. The combined values registered in the counters represent the shaft position code. The inherent uncertainty in recognizing when the "slow" counter should register any particular value represented by the position of its selector along its series of elements could create significant ambiguity, which is here resolved through use of the value registered in the counter of the "fast" series of elements.
The prior art teaches a variety of encoders and measurement systems. However, the prior art does not teach that such a system may provide a press roll in compressive contact with a linear moving control bar wherein the control bar is engraved by the press roll during an initial linear pass and thereafter remains in sync therewith due to continued engagement of the engraving. The present invention fulfills these needs and provides further related advantages as described in the following summary.